class Track: public TObject

                       Event and Track classes


  The Event class is a naive/simple example of an event structure.
     public:
        char           fType[20];
        char          *fEventName;         //run+event number in character format
        Int_t          fNtrack;
        Int_t          fNseg;
        Int_t          fNvertex;
        UInt_t         fFlag;
        Double32_t     fTemperature;
        Int_t          fMeasures[10];
        Double32_t     fMatrix[4][4];
        Double32_t    *fClosestDistance; //[fNvertex] indexed array!
        EventHeader    fEvtHdr;
        TClonesArray  *fTracks;
        TRefArray     *fHighPt;            //array of High Pt tracks only
        TRefArray     *fMuons;             //array of Muon tracks only
        TRef           fLastTrack;         //pointer to last track
        TRef           fHistoWeb;          //EXEC:GetHistoWeb reference to an histogram in a TWebFile
        TH1F          *fH;
        TBits          fTriggerBits;       //Bits triggered by this event.

   The EventHeader class has 3 data members (integers):
     public:
        Int_t          fEvtNum;
        Int_t          fRun;
        Int_t          fDate;


   The Event data member fTracks is a pointer to a TClonesArray.
   It is an array of a variable number of tracks per event.
   Each element of the array is an object of class Track with the members:
     private:
        Float_t      fPx;           //X component of the momentum
        Float_t      fPy;           //Y component of the momentum
        Float_t      fPz;           //Z component of the momentum
        Float_t      fRandom;       //A random track quantity
        Float_t      fMass2;        //The mass square of this particle
        Float_t      fBx;           //X intercept at the vertex
        Float_t      fBy;           //Y intercept at the vertex
        Float_t      fMeanCharge;   //Mean charge deposition of all hits of this track
        Float_t      fXfirst;       //X coordinate of the first point
        Float_t      fXlast;        //X coordinate of the last point
        Float_t      fYfirst;       //Y coordinate of the first point
        Float_t      fYlast;        //Y coordinate of the last point
        Float_t      fZfirst;       //Z coordinate of the first point
        Float_t      fZlast;        //Z coordinate of the last point
        Double32_t   fCharge;       //Charge of this track
        Double32_t   fVertex[3];    //Track vertex position
        Int_t        fNpoint;       //Number of points for this track
        Short_t      fValid;        //Validity criterion
        Int_t        fNsp;          //Number of points for this track with a special value
        Double32_t  *fPointValue;   //[fNsp] a special quantity for some point.
        TBits        fTriggerBits;  //Bits triggered by this track.

   An example of a batch program to use the Event/Track classes is given
   in this directory: MainEvent.
   Look also in the same directory at the following macros:
     - eventa.C  an example how to read the tree
     - eventb.C  how to read events conditionally

   During the processing of the event (optionally) also a large number
   of histograms can be filled. The creation and handling of the
   histograms is taken care of by the HistogramManager class.

   Note:  This version of the class Event (see EventMT.h and EventMT.cxx
   for an alternative) uses static variables to improve performance (by
   reducing the number of memory allocations).  Consequently, only one
   instance of the class Event should be in use at a time (a 2nd instance
   would share the array of Tracks with the first instance).